Miniature photocells and method op making the same



Sept. 21, 1965 P. STROTHER MINIATURE PHOTOCELLS AND METHOD OF MAKING THE SAME Original Filed Jan. 4. 1960 2 Sheets-Sheet 1 FIGJ.

INVENTOR FRED R STROTHER ATTORNEYS Sept 21, 6 F. P. STROTHER MINIATURE PHOTOCELLS AND METHOD OF MAKING THE SAME Original Filed Jan. 4, 1960 2 Sheets-Sheet 2 FIG.8.

INVENTOR FRED P. STROTHER ATTORNEYS United States Patent 3,206,831 MINIATURE PHOTOCELLS AND METHOD OF MAKING THE SAME Fred P. Strother, Shawmut, Ala., assignor to West Point Manufacturing Company, West Point, Ga., 21 corporation of Georgia Original application Jan. 4, 1960, Ser. No. 405, now Patent No. 3,069,487, dated Dec. 25, 1962. Divided and this application Apr. 28, 1961, Ser. No. 111,889

Claims. (Cl. 29-1555) This application is a division of my copending application, Serial No. 405, filed January 4, 1960, now US. Patent No. 3,069,487, granted December 25, 1962, and is entitled to the filing date thereof.

This invention relates to photocells, and in particular to miniature photocells adapted to be positioned in locations of difficult access. The invention relates also to groups of miniature photocells arrayed in close order, and to methods of making the photocells.

A principal object of the invention is the provision of multiple photocells of miniature size, adapted for use in automation, data reduction, process control and the like where operation or control by means of a number of closely spaced and individual photocells is desired. Another object of the invention is to provide a compact photocell unit comprising large numbers of closely spaced and individual photocells, which may be arranged in line or in two-dimensional arrangement. In accordance with the present invention, for example, it is possible to provide a photocell array comprising more than 250,000 individual photocells per square inch.

A further object of the invention is the provision of a miniature photocell which may be operatively positioned in ordinarily inaccessible places, for example within the human body, which photocell is both rigid and selfsupporting. Other objects of the invention are the provision of novel miniature photocells and miniature photocell arrays wherein electrical connection to each individual photocell may be readily made in simple, quick fashion. The photocells, further, lend themselves to simplified and inexpensive manufacture, by mass production methods.

Other objects of the invention are to provide novel methods of manufacturing miniature photocells and miniature photocell arrays, by simple and economical procedures. Further objects of the invention will be in part evident, and in part pointed out hereinafter.

The invention and the novel features thereof may best be made clear from the following description and the accompanying drawings, in which:

FIGURE 1 is an elevational sectional view of an exemplary embodiment of the present invention, on enlarged and exaggerated scale, taken on the line 11 of FIGURE 2;

FIGURE 2 is a transverse sectional view taken on the line 22 of FIGURE 1;

FIGURE 3 is a diagrammatic view illustrating a simplified method for initially arranging a plurality of wires for incorporation into a rigid matrix;

FIGURE 4 is an elevational sectional view of another embodiment of the invention, taken on the line 4-4 of FIGURE 5;

FIGURE 5 is a transverse sectional view taken on the line 5-5 of FIGURE 4;

3,206,831 Patented Sept. 21, 1965 FIGURES 6-9 are a series of views illustrating one mode of manufacture of a modified photocell in accordance with the invention. FIGURE 6 is an elevational sectional view of a single wire embedded in a metal tube, the assembly being faced off flush in a plane perpendicular to the wire axis;

FIGURE 7 is a view of the assembly of FIGURE 6, after the metal tube end has been extended beyond the enclosed wire and insulation by coating;

FIGURE 8 is a view of the assembly of FIGURE 7 after the face end thereof has been coated with photosensitive material;

FIGURE 9 illustrates the condition of the FIGURE 8 assembly, after removal of all photosenstive material except from the recessed insulated wire end;

FIGURE 10 is an elevational sectional view of a photocell array comprising units of the type illustrated in FIG- URE 9, taken on the line 10-10 of FIGURE 11, and

FIGURE 11 is a face end view of the photocell array of FIGURE 10.

In the drawings, FIGURES 1 and 2 illustrate a simple embodiment of the present invention, wherein a plurality of insulated Wires 20, each bearing an insulating coating 22 thereon, are arranged in closely spaced parallelism and embedded in a conductive matrix 24. The wires 20 may be commercial copper wire of small diameter, for example .001 inch diameter, and spaced apart from each other about .001 inch, whereby 500 wires may be arranged to the lineal inch, or 250,000 to the square inch.

It will be understood that wires of smaller diameter may be employed with less spacing therebetween, whereby arrays with 1,000 or more to the inch may be constructed. The conductive matrix 24 may be composed of low melting alloy, or may be resin filled with a large proportion of conductive particles, such as metal or carbon. Common aldehyde resins highly filled with metal or carbon particles are entirely suitable.

In the embodiment illustrated, corresponding ends 26 of the wires 20 terminate flush with the surface 28 of the matrix, the surface 28 being preferably normal to the wire axes. As will be understood, the surface 28 may be planar, curved or otherwise.

As illustrated in FIGURE 1, the matrix surface 28 and wire ends 26 are coated with a layer 30 of photosensitive material. The free wire ends 32 may be of any desired length, and are adapted to be separated from their fellows and individually connected to different circuits. The conductive matrix 24 serves as a common terminal, and electrical connection thereto may be made in any conventional fashion, as by soldering wire thereto. As will be understood, each free wire end 32 constitutes the other terminal of an individual photocell, and may be connected to its own circuit. Each individual photocell is in essence a ring of photosensitive material extending between a wire end and the surrounding matrix, over the insulating coating 22 of-the wire. As the photosensitive material layer 30 has finite thickness, there is a certain amount of dispersion of electrons therein as Well as of the light entering the material, whereby the described assembly approximates a point form if the overall diameter is quite small; that is, the cell functions in the manner of a disc, rather than as a ring.

The wires 20 may be arranged in closely spaced parallelism, and then maintained or fixed in such relationship by application of the conductive matrix to the assembly.

One simple procedure is arranging the wires as illustrated in FIGURE 3, wherein is utilized a relatively large diameter cylinder 34 provided with a longitudinal recess 36, in the shape of a keyway, extending along a side thereof. As illustrated, a continuous Wire 38 may be wound about the cylinder 34 with desired spacing between adjacent convolutions. In using insulated wire, no spacing is required, and the convolutions may be wound side by side. If greater spacing is desired, it may be readily effected by appropriate grooving or threading on the cylinder 34, or two wires 38 may be wound simultaneously side by side, and one subsequently removed to leave the other in desired spaced relationship.

After the desired number of convolutions are wound, the wire layer may be embedded in the matrix by applying the matrix to the wire layer in and above the recess 36. As will be evident, the wire sections extending across the recess are necessarily straight and parallel. The matrix may be appropriately set or hardened after application, whereupon the wire layer may be cut above either edge of the recess 36, the wire layer thereby yielding a very large number of closely spaced wires embedded at one end in the matrix. The diameter of the cylinder 34 will determine the length of the free wire ends. The sub-assembly may then be ground or buffed on its end surface corresponding to the cut line previously referred to, whereby the Wire ends 26 and matrix surface 28 are made flush, and lie in a common plane, as illustrated in FIGURE 1.

The photosensitive layer 30 is next applied to the surface composed of the matrix and the wire ends 26. Any material having photosensitive characteristics may be employed, including photo-resistive, photo-voltaic and photo-emissive materials. Suitable materials, for example, include cadmium sulphide, cadmium selenide and antimony trisulphide. The coating may be applied in any manner adapted to effect a uniform thin material layer, including by evaporation, settling, spraying and the like. For the purposes of the present invention, it is preferred that the photo-sensitive layer 30 be so thin as to be light permeable. That is, in use some light must completely penetrate the layer 30 in order to provide requisite electron excitation. The term light is used as inclusive of radiation of any wave length covering the entire range from ultra-violet to infra-red.

The preferred method of applying the photo-sensitive material layer 30 is by sputtering or evaporation in a vacuum. In the case of cadmium selenide, for example, a layer thickness of the order of .0001 inch is useful, and the application may be controlled by evaporating a predetermined quantity of material under established conditions, or by utilizing a glass plate as a visual control, the proper thickness of coating being detected by color change of the control plate.

If the photosensitive material is applied otherwise than by evaporation, it may be necessary to consolidate or sinter the photosensitive material layer, and this is accomplished advantageously by heating the coated assembly after application of the coating material to appropriate temperature. The photosensitive layer may then be sensitized by any conventional and appropriate method, e.g. by treatment with halogens and copper salts.

In the case of some photosensitive materials, it is advantageous to subject the material after application to ionic bombardment in a vacuum, to improve or modify the final characteristics of the photocells. Typically, such bombardment may be carried out for a period of from about 30 seconds to about 2 minutes under a pressure of the order of 1 mm. of mercury. In the present case, if the photosensitive material is applied by evaporation, the bombardment may be conveniently effected before removal from the vacuum chamber.

In some applications, it is desirable that the face contact between the photosensitive material and the wires be ohmic or non-rectifying in character. This can be effectively accomplished by providing an extremely thin flash coating of indium or gallium therebetween, conveniently in the vacuum coating step.

Application and sensitization of the photosensitive material layer completes the manufacture of the photocell array. As previously indicated, the conductive matrix 24 serves as a common terminal, and connection to each idividual photocell may be made through the individual free wire ends 32, the photosensitive material lying immediately over each wire end 26, including its insulation, functioning as an individual photocell. While in the example the photosensitive layer 30 is continuous, the relative resistance between one cell and adjoining cells is so great that the array functions substantially as if the photosensitive layer were discontinuous between cells.

In the above description of the winding operation, winding a single wire layer will effect a photocell array in in-line arrangement. Two dimensional arrangements may be produced in similar fashion. For example, in winding insulated wire without spacing, a plurality of wire layers may be wound, one on another. If the winding is with spacing, similar spacing between successive layers may be achieved by interposing thin sheets of matrix material. In this manner, a uniformly spaced arrangement may be effected as illustrated in FIGURE 2.

In accordance with another embodiment of the invention, each wire 20 may be imbedded inside a metal tube, by means of a cement or similar material. Stainless steel tubing, for example, is commercially available in sizes as small as .005 inch in outer diameter, whereby they may be arranged 200 to the inch in line and in twodimensional array. FIGURES 4 and 5 illustrate a miniature photocell array wherein each uninsulated wire 40 is cemented in a metal tube 42 by means of a cement 44. Necessarily, if u-ninsulated wires are used, the cement 44 should be an electrically insulating cement, such as ceramic cement, epoxy resin or the like. If the wires are insulated, any suitable cement may be employed. Each wire may be readily and eifectively centered and cemented in its associated tube by initially passing the wire through the tube, applying a drop of cement material to the protruding wire end, and then drawing the wire end back into the tube. The cement material, if of proper consistency, will completely surround the wire within the tube, and on appropriate hardening of the cement material, the wire will be securely mounted in and electrically insulated from the tube. Another procedure is to apply a drop of the cement material to the wire end or to the tube end, and then insert the Wire into the tube.

The metal tubes, each with a wire mounted therewithin, may then be positioned side by side in desired arrangement, with their corresponding ends substantially aligned and embedded in a conductive matrix material adapted to maintain the array in desired relationship. Since the tubes are metal, common solder is a particularly convenient matrix material. After the matrix has hardened, the surface 46 of the assembly may be ground or otherwise leveled otf, whereby the tube ends and wire ends are made flush, whereupon the photosensitive material layer 30 may be applied thereto as previously described. As in the embodiment of FIGURES 1 and 2, the matrix serves as a common terminal and each free wire end 32 as the other terminal of an individual photocell.

As will be evident, the miniature photocells of the array of FIGURES 4 and 5 may be manufactured and utilized as individual photocells. This involves merely embedding a single wire in a tube as described, grinding an end flush, and applying photosensitive material to the flush end. The photocell is rigid and self-supporting, and may be readily disposed or mounted in many locations of difficult access, by means of the metal tube. Electrical connection to the miniature photocell offers no difficulty, the tube serving as one terminal and the free end of the wire serving as the other.

The photocells illustrated in FIGURES 4 and 5, in dividually or in arrays, may be modified in accordance with the procedure described in connection with FIG- URES 6-9, this representing a somewhat more sensitive and efficient construction. FIGURE 6 illustrates an individual photocell comprising an uninsulated wire 40 embedded in a metal tube 42 by means of an insulating cement 44, the outer surface 46 being ground flush. The assembly is then treated to recess the Wire 40 and insulation 44 slightly within the metal tube 42, to form a shallow pocket 48 above the end of the insulated wire, as illustrated in FIGURE 7. This may be accomplished by mechanically removing the exposed end of the wire and insulation to the required depth, or more conveniently by extending the metal tube by coating additional metal thereonto. The coating of additional metal onto the exposed end of the metal tube may be accomplished most readily by selective electrodeposition of metal onto the end of the metal tube, to the exclusion of the insulated wire end, either in solution or in a vacuum. Deposition of metal onto the insulation wire end may be prevented by masking, or more conveniently by maintaining the metal tube at a potential different from that of the Wire and insulation.

The photosensitive layer 30 may then be applied as previously described, the resultant coating, as illustrated in FIGURE 8, filling the pocket 48 and overlying the tube end. As will be recognized, the depth of the pocket 48 may be predetermined to correspond to the desired thickness of photosensitive material, and the applied layer of photosensitive material may then be buffed or similarly mechanically finished down to the tube end, leaving, as illustrated in FIGURE 9, a thin disc 50 of photosensitive material in the pocket 48. The photosensitive material disc 50 may thereafter be sensitized and processed as previously described. As will be understood, this construction is advantageous in that the tube wall enclosing the pocket 48 functions as a lateral light barrier for the enclosed disc 50.

Photocells of the type illustrated in FIGURES 69 may, of course, be constructed in the form of a photocell array, as illustrated in FIGURES 10 and 11. This may be done, in accordance with one exemplary procedure, by arranging a plurality of the metal tubes, each with a wire mounted therewithin, in substantial alignment, and embedding the tubes in a conductive matrix such as solder. The assembly may be finished flush, and recessing of the insulated wire ends accomplished as by coating metal onto the exposed matrix surface, including primarily the metal tube ends. The photosensitive layer may then be applied and removed at the level of the tube ends, leaving a thin disc 50 of photosensitive material in each pocket 48 overlying an insulated wire end. The photosensitive material discs 50 may thereafter be sensitized and processed as previously described, in a single operation. FIGURES 10 and 11 illustrates a closely packed array, wherein adjacent metal tubes 42 are substantially in contact. As previously described, the tube walls enclosing the pockets 48 function as light barriers with respect to the photosensitive discs 50, contributing materially to improved sensitivity and efiiciency.

It will thus be seen that there has been provided by this invention an article and method in which the various objects hereinbefore set forth, together with many practical advantages, are successfully achieved. As various possible embodiments may be made of the novel features of the above invention, all without departing from the scope thereof, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative, and not in a limiting sense.

I claim:

1. Method of making a miniature photocell array comprising Winding a plurality of insulated wires upon a mandrel to form a helix having a plurality of close fitting substantially parallel convolutes, embedding said convolutes in a hardenable conductive binder material, hardening said material to provide a rigid conductive binder, cutting through said convolutes in a direction substantially normal to the direction of wind of said convolutes to provide a binder surface normal to the wire axes, removing said cut bound convolutes from said mandrel, said conductive binder constituting a common terminal for the individual photocells of the array, removing insulated wire ends protruding from said binder so that said insulated wires provide a common surface with said binder material, said common surface being generally transverse with respect to the wire axes and applying a thin layer of photosensitive material to said common surface.

2. Method of making a miniature photocell array comprising the steps of winding a plurality of insulated wires upon a mandrel to form a helix having a plurality of close fitting substantially parallel convolutes, embedding the insulated wires in a hardenable conductive binder material, hardening said material to provide a rigid conductive binder, said conductive binder constituting a common terminal for the individual photocells of the array, cutting through said convolutes in a direction substantially normal to the direction of wind of said convolutes to provide a binder surface normal to the wire axes, removing said out bound convolutes from said mandrel, removing insulated wire ends protruding from said binder so that said insulated wires provide a common surface with said binder material, said common surface being generally transverse with respect to the wire axes and recessing said wires and insulation to form a shallow pocket in said common surface and applying a thin layer of photosensitive material to the recessed ends of said wires and insulation.

3. Method of making a miniature photocell array comprising the steps of winding a plurality of wires upon a mandrel to form a helix having a plurality of close fitting substantially parallel convolutes, embedding the insulated wires in a hardenable conductive binder material, hardening said material to provide a rigid conductive binder, cutting through said convolutes in a direction substantially normal to the direction of wind of said convolutes to provide a binder surface normal to the wire axes, removing said cut bound convolutes from said mandrel said conductive binder constituting a common terminal for the individual photocells of the array, removing insulated wire ends protruding from said binder so that said insulated wires provide a common surface with said binder material, extending said binder with respect to the insulated wire ends whereby a shallow pocket is formed above the end of each insulated wire, and applying a thin layer of photosensitive material to the recessed ends of said wires and insulation.

4. Method of making a miniature photocell array comprising the steps of embedding a plurality of insulated wires each within a metal tube, arranging said tubes in closely spaced parallelism, fixing said tubes in such arrangement while maintaining electrical connection therebetween, whereby said tubes constitute a common terminal for the individual photocells of the array, machining said assembly so that said insulated wires and said tubes terminate in a common surface generally transverse with respect to the wire axes, extending the tube ends by coating metal thereonto, whereby a shallow pocket is formed above the end of each insulated wire, applying a thin layer of photosensitive material overlying the extended tube ends and said pockets, and mechanically removing the photosensitive material from said tube ends to leave a small disc of photosensitive material in the pocket overlying each insulated Wire end.

5. A method of making a miniature photocell array comprising the steps of embedding a plurality of insulated wires each within a metal tube, arranging said tubes in closely spaced parallelism, fixing said tubes in such ar- References Cited by the Examiner UNITED STATES PATENTS 1,935,649 11/33 McCreary 338-47 Betzler 138-89 X Gier 29155.57 X Pantchecknikotf.

Raymer 29155.7 McIlvaine 13889 X Cole.

Coler 29155.5 Harmon et al. 29155.5

10 WHITMORE A. WILTZ, Primary Examiner.

JOHN P. CAMPBELL, Examiner. 

1. A METHOD OF MAKING A MINIATURE PHOTOCELL ARRAY COMPRISING WINDING A PLURALITY OF INSULATED WIRES UPON A MANDREL TO FORM A HELIX HAVING A PLUARALITY OF CLOSE FITTING SUBSTANTIALLY PARALLEL CONVOLUTES, EMBEDDING SAID CONVOLUTES IN A HARDENABLE CONDUCTIVE BINDER MATERIAL, HARDENING SAID MATERIAL TO PROVIDE A RIGID CONDUCITVE BINDER, CUTTING THROUGH SAID CONVOLUTES IN A DIRECTION SUBSTANTIALLY NORMAL TO THE DIRECTION OF WIND OF SAID CONVOLUTES TO PROVIDE A BINDER SURFACE NORMAL TO THE WIRE AXES, REMOVING SAID CUT BOUND CONVOLUTES FROM SAID MANDREL, SAID CONDUCITVE BINDER CONSTITUTING A COMMON TERMINAL FOR THE INDIVIDUAL PHOTOCELLS OF THE ARRAY, REMOVING INSULATED WIRE ENDS PROTRUDING FROM SAID BINDER SO THAT SAID INSULATED WIRES PROVIDE A COMMON SURFACE WITH SAID BINDER MATERIAL, SAID COMMON SURFACE BEING GENERALLY TRANSVERSE WITH RESPECT TO THE WIRE AXES AND APPLYING A THIN LAYER OF PHOTOSENSITIVE MATERIAL TO SAID COMMON SURFACE. 